The present invention relates to combustion engine driven heat pump systems and air conditioning systems which provide for the auxiliary generation of electrical power. In particular, it relates to those systems which generate auxiliary electrical power for system fans and pumps, for building power requirements, or for return to power system grids.
This invention is directed primarily to heat pump systems which are applied to heating and air conditioning loads of the environment in the living spaces of buildings. As used herein, the term air conditioning means the adjustment of the temperature and humidity in the living space to selected comfortable norms when the outside environment and particularly the ambient temperature, is either too high or too low for comfort. However, many of the objectives and concepts of this invention also have application to other types of thermal loads. Therefore, the term "load" as used herein, while specifically in the context of air conditioning, may be interpreted broadly to apply to other thermal loads by those familiar with heating and cooling technology.
In many heat pump systems, refrigerant vapor is compressed in rotating or reciprocating compressors. Where the compressor is driven by an internal combustion engine or other form of motive power, it has been proposed to further connect and drive an electrical generator with the engine to produce auxiliary power.
The co-generation of electrical power in heat pump systems presents various problems, including the maintenance of constant electrical output, typically 60 cycle alternating current. To produce 60 cycle alternating current power, it is typically necessary that the generator be operated at substantially constant speed. Because of the wide range of temperature and load conditions to which the heat pump system responds, the demand on the combustion engine will vary dramatically with the compressor load. Consequently, engine throttle and speed are important factors which must be controlled to achieve both proper heat pump system operation and proper electrical generation.
U.S. Pat. No. 4,991,400 to Wilkinson discloses an apparatus providing for interconnection and cooperation between the various heat pump and electrical generation components of the system which provides for more optimal, and continuous operation of both the heat pump and electrical generation systems. In the '400 patent, Wilkinson teaches the use of a continuously variable transmission (CVT) to continuously vary, increasing or decreasing, the ratio of speed between the combustion engine and the electrical generator. A planetary gear is further positioned at the compressor in cooperation, the CVT to further increase or decrease the speed and torque transmitted to the compressor.
While the CVT is capable of providing continuous, generally constant operation of the electrical generator and continuous operation of the compressor, these components can add considerable cost to the overall heat pump/power generation system. Moreover, the added complexity increases the maintenance requirements of the heat pump system, such as the need to maintain the belts of belt-driven CVTs. The continuous production of electrical power, while desirable, has the undesirable effect, particularly in extreme temperature conditions, of requiring additional loading of the combustion engine at times when it already experiences high loads at the compressor. Moreover, despite the use of the CVT and planetary gear, the compressor typically continues to provide some load to the combustion engine at all times, reducing the overall efficiency of the system.
Accordingly the need remains for additional, cost-effective, reliable heat pump systems providing electrical co-generation, without the disadvantages of existing systems.